Summary Precise metabolic phenotyping depends significantly on the health status of animal subjects. Traditionally, the ?Animal Care Core? has focused on providing stable housing and husbandry and microbiological testing to minimize the influence of exogenous factors that could impact phenotyping results. However, an increased understanding of the microbiome and its potentials impact on physiologic processes has prompted the ?Animal Care Core? to establish strong ties with Dr. Andrew Goodman (Associate Professor of Microbial Pathogenesis), a microbiome and gnotobiotics expert at Yale. Under co-directors Macy and Goodman, the core will become the ?Microbiome and Animal Care Core? to reflect expansion of its mission to include compositional and functional analysis of the microbiome. Assessing the impact of microbiome in the context of a metabolic phenotype is an important, if not transformative step in unraveling the mechanistic processes that define a metabolic phenotype. The rationale for consolidating these core functions within the Animal Care Core was discussed and approved by the NIDDK Program Staff. The Core will continue to provide state-of-the-art husbandry, health care, quarantine, testing, and procedure space and utilize its expedited quarantine program that has supported the MMPC during the past 12 years. This approach has successfully decreased the quarantine time and allowed phenotyping to begin while animals are within quarantine, allowing animals to be studied at younger ages and minimizing costs associated with the phenotyping process. The microbiome component of the core will advance metabolic phenotyping by offering: 1) compositional profiling and metagenomic characterization of the microbiome of the gastrointestinal tract in subject animals and their wildtype littermates; 2) metabolic phenotyping of subject animals, their wildtype littermates, and wildtype germfree controls after each group has been exposed to broad-spectrum antibiotic cocktails; 3) fecal microbiome transplantation services into germfree recipient animals, followed by metabolic and microbiome phenotyping, to provide definitive evidence of the ability of a subject animal microbiome to confer a metabolic impact on its host. The Microbiome and Animal Care Core will continue to utilize dedicated biocontainment housing and procedure space and will add fully operational, state-of-the art gnotobiotics and microbiome profiling capabilities in place in the Goodman laboratory. In parallel, the Animal Resource center also operates a well-established gnotobiotic housing facility adjacent to Dr. Goodman's facility in which there is a history of sharing resources for operating these two facilities, thereby adding capacity and redundancy to support the Yale MMPC.